1. Meiosis
Ch. 11-4

2. Asexual Reproduction Offspring can be reproduced from one parent
Budding (sponges)
Regeneration (sea stars)
Grafting (in trees and plants)
Binary Fission/Mitosis (unicellular animals)
In this situation, offspring are genetically identical to their parent

3. Sexual Reproduction Produces offspring by union of gametes
Gamete: a sex cell (like a sperm or egg)
Allows for genetic variability
Allows for evolution to occur
Variety of genes available to an organism allows it to adapt to various situations.

4. Meiosis Cell division process that takes place only in gametes
DNA copies during interphase
Cell divides once (meiosis 1)
Cell divides again (meiosis 2)
Result is 4 haploid cells

5. Meiosis

6. Meiosis 1 Prophase 1 DNA coils up Spindle appears
Cell Membrane
Centrioles
Prophase 1
DNA coils up
Spindle appears
Nucleolus & Nuclear Membrane disappear
Chromosomes line up with their partner
Crossing over can occur
Spindle
(forming)
Tetrad
Nucleus
(fading)

7. Synapsis Happens during Prophase 1
Synapsis: Two like chromosomes line up beside one another
They are now called tetrads

8. Crossing Over Happens during Prophase 1
When synapsis occurs, chromosome arms wrap around one another
Sometimes arms break and join the opposite chromosome.

9. Crossing Over Crossing Over exchanges DNA between like chromosomes
The result of crossing over is Genetic Recombination and increased genetic variability
This leads to evolution…

10. Metaphase 1 Spindle is fully formed
Centrioles
Cell Membrane
Spindle is fully formed
Tetrads line up across the center of the cell
Their arrangement on the spindle is random!!
Spindle
(complete)
Tetrad
**Notice – there is NO nucleus present here!

11. Anaphase 1 Tetrads are pulled to opposite ends of the cell
Centrioles
Chromosomes
Tetrads are pulled to opposite ends of the cell
Chromosomes are randomly separated!
Separating
Spindle

12. Independent Assortment
Chromosomes are randomly lined up and pulled apart during meiosis.
Which daughter cell receives which chromosomes is not controlled, so it is called independent assortment.
The result is increased genetic variability!

13. Independent Assortment

14. Telophase 1 Cell divides into two new cells The cells are diploid
Centrioles
Chromosomes
Cell divides into two new cells
The cells are diploid
Cleavage Furrow

15. Meiosis 2 Meiosis 2 proceeds much like mitosis.
DNA does not copy before prophase 2
The end result is 4 haploid sex cells

16. Prophase 2 Spindle fibers appear Nucleus and Nucleolus are not visible
Centrioles
Spindle fibers appear
Nucleus and Nucleolus are not visible
Chromosomes

17. Metaphase 2 Spindle is completely formed
Centrioles
Spindle is completely formed
Chromosomes line up across the center of the cell
Chromosomes

18. Anaphase 2 Spindle separates chromosomes
Spindle (separating)
Centrioles
Spindle separates chromosomes
Chromosomes are pulled to opposite ends of the cell.
Chromatids

19. Telophase 2 Spindle disappears Chromosomes relax Cytokinesis occurs
Cell Membrane
Centrioles
Spindle disappears
Chromosomes relax
Cytokinesis occurs
Nuclear membrane & Nucleolus reform
Nucleus
Cleavage Furrow
Chromatin (haploid #)

20. Mitosis vs. Meiosis

21. Mitosis vs. Meiosis

22. Gametogenesis Gametogenesis: formation of gametes
Spermatogenesis: makes sperm in the testes
Oogenesis: makes eggs in the ovaries (ova)

23. Spermatogenesis Meiosis occurs in the testes Result is 4 haploid sperm
All 4 sperm will mature and grow tails

24. Oogenesis Meiosis occurs in the ovaries
Cytoplasm divides unequally in the cells
Result is 1 haploid ova and 3 polar bodies
The ova will mature
The polar bodies will disintegrate and die

25. The End